HI Tan, I had the same problem with this baby. Like you he is my third. My first child I didn't feel until 18 weeks, but my second child I felt at 14 weeks. This one I didn't feel until about 18 weeks again. I think it can have something to do with the placement in the uterus (if it is on the back wall then movement can take a while to feel).
If you are really worried though, go see your doc. A simple us will put your mind at rest.